Channel letters are used to provide signage for buildings, shopping malls, and the like where it is desirable that the signage comprises illuminated letters or any other shapes that are easily seen, even at great distances, day or night. Each channel letter generally comprises an enclosure usually a metal box, having a rear surface which is positioned against a raceway, or the wall of a building, on which the signage is mounted and a plurality of sides which define the figuration of a letter, number or symbol which make up a portion of the sign. A light source, such as a neon tube, fluorescent tube or a series of light-emitting diodes (LEDs) is positioned within the walls of the enclosure and attached to the rear surface to provide illumination for the letter. The enclosure typically has one translucent surface through which the light is emitted.
When LEDs are used as the light source in channel letters, they effectively behave as point sources, thus creating bright, localized regions referred to as hot spots that are visible through the translucent surface. Such hot spots are distracting and aesthetically displeasing. This effect has been reduced by the use of diffuse films, for example, as disclosed in U.S. Pat. No. 6,641,880. Conventional channel letter LED systems, which typically use surface mounted LEDs on a printed circuit board (PCB) with little or no optics as illustrated in FIG. 1. These systems however, rely on the highly reflective surfaces of the adjacent walls 20 to transfer the light from the LEDs 22 to the emitting surface 21 as illustrated in FIG. 2. The problem with this type of system is that over time the surfaces of the walls can be contaminated with dirt or debris due to water ingress, for example. This can lower the reflectivity of the wall material and thus reduce the amount of reflected light from the LEDs or other light source to the translucent emitting surface.
FIG. 3 illustrates a beam pattern 34 typically produced by LEDs 32, wherein this beam pattern is radially symmetrical. When these LEDs are positioned within a channel letter application, they typically do not provide sufficient uniformity of illumination for the entire channel letter, thereby resulting in dark regions 36. In order to reduce the size of these dark regions, the LEDs can be closely spaced together, however this closer proximity of the LEDs may not be desired. Furthermore, when high flux LEDs are used for channel letter applications, typically fewer LEDs are used to illuminate a channel letter due to the higher level of irradiation generated by these devices. With a reduction in the number of LEDs 42 that produce radially symmetrical beam patterns 44 for illuminating a channel, extreme darks regions 46 may result as illustrated in FIG. 4.
In addition, for narrow channel letters, as is common with letters formed using serif fonts, for example, it can be difficult to fill the narrow regions of this type of letter with light due to its tight geometry as illustrated by locations 30 in FIG. 5.
Some manufacturers offer an optic or lens, which alters the beam angle such that the number of interactions of light rays striking the wall surface is reduced. However, this configuration typically does not provide sufficient light to the narrow regions of channel letters. In addition, these forms of optics typically increase the beam angle of the emitted radiation in a radially symmetrical fashion.
U.S. Pat. No. 6,566,824 references a technique that utilizes an optical element in front of the LED to vary the spread of the emitted light. The optical element is essentially an encasing around the LED where, for example, conventional bullet-shaped lenses, flat tops and BugEye™ lenses are used as the optical element.
U.S. Pat. No. 6,416,200 discloses a technique for illuminating the tread area and the edges of steps or stairs, especially in business establishments such as theatres and restaurants, where the steps or stairs may be in dark or dimly light areas. This technique however, provides a means for detachably mounting a light strip assembly to enable angular adjustment of the emitted light through a predetermined angle.
In addition, Fraen Corporation manufactures an optic that collimates light and this product is illustrated in FIGS. 6a and 6b. Light from an LED strikes two front surfaces, one being spherical 32 and the other being conical 34. Light striking the spherical surface is collimated and light striking the conical surface is refracted and subsequently strikes the parabolic surfaces 36 of the optic. This light total internally reflects within the optic thereby providing a collimated beam of light. Additionally, as illustrated in FIG. 6b an additional optical element may be included wherein this additional optic can be a concave surface 38 which can be used to produce an elliptical beam distribution. These optical configurations however, do not provide sufficient light or illumination to areas with tight geometries, for example, however this product may be used in a light grazing application.
Grazing luminaries illuminate a surface that is parallel to the general direction of the emitted light. Aesthetics can demand that the luminaire be placed as close as possible to the surface to be illuminated. This configuration can pose a challenge as most optics are designed to distribute light symmetrically around at least one axis, resulting in wasted light that does not reach the surface to be illuminated. The conventional solution to this problem is to angle the light source towards the surface, resulting in more light reaching the surface. This solution however, is not optimal as it creates a non-uniform wash of light that can result in a hot spot located at the centre axis of the beam distribution pattern.
Therefore, there is a need for an apparatus and method for forming an asymmetric illumination beam pattern thereby enabling for example, the illumination to tight geometry areas and/or increasing the efficiency of emitted light in applications such as channel letters, in addition to enabling the generation of uniform illumination of a surface in close proximity to the light sources.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.